Wear resistant frictionally contacting surfaces

ABSTRACT

An improved mechanical system comprising a first part presenting an aluminum surface, a second part presenting a second surface capable of being in sliding contact with the aluminum surface, and means for inducing and maintaining the two surfaces in sliding contact with each other, for example, an hydraulically operated piston-cylinder mechanical system, the improvement consisting of employing as the second surface a metallic surface comprising an alloy containing at least 60 atom percent of at least two heavy metal transition elements, the ratio of the atomic radii of the largest to the smallest transition elements being 1.05-1.68, and consisting of 10-100 volume of a hard phase and 0-90 volume percent of a matrix phase which is softer than the hard phase, said hard phase containing a major fraction of Laves phase in such amount as to provide at least 10 volume percent thereof in the alloy.

Tlite States Calabrese I atent [191 WEAR RESISTANT FRICTIONALLY CONTACTING SUACES Salvador-e Joseph Calabrese, Troy, NY.

[73] Assignee: E. 1. DuPont de Nemours and Company, Wilmington, Del.

[22] Filed: Oct. 19, 1972 [21] Appl. No.: 298,838

[75] Inventor:

[52] 11.8. C1 308/241, 4l7/DIG. 1, 418/179 [51] Int. Cl. F16c 33/12 [58] Field of Search 418/177, 179; 308/8, 241; 417/DIG. 1

[56] References Cited UNITED STATES PATENTS 3,289,649 12/1966 Lamm 418/178 X 3,318,515 5/1967 Jones i 418/179 X 3,359,953 12/1967 Groth 418/179 X 3,361,560 [/1968 Sevems, Jr. ct a1. 75/170 3,552,895 1/1971 Bayley 418/178 3,795,430 3/1974 Farley 308/241 R2493). 1/1961 Davey 418/178 X Primary ExaminerC. J. Husar Assistant Examiner-Leonard Smith 5 7 ABSTRACT An improved mechanical system comprising a first part presenting an aluminum surface, a second part presenting a second surface capable of being in sliding contact with the aluminum surface, and means for inducing and maintaining the two surfaces in sliding contact with each other, for example, an hydraulically operated piston-cylinder mechanical system, the improvement consisting of employing as the second surface a metallic surface comprising an alloy containing at least 60 atom percent of at least two heavy metal transition elements, the ratio of the atomic radii of the largest to the smallest transition elements being 1.05-1.68, and consisting of 10-100 volume of a hard phase and 0-90 volume percent of a matrix phase which is softer than the hard phase, said hard phase containing a major fraction of Laves phase in such amount as to provide at least 10 volume percent thereof in the alloy.

10 Claims, 6 Drawing Figures WEAR RESISTANT FRICTIONALLY CONTACTING SURFACES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to metallic mechanical systems comprising two opposing surfaces maintained in frictional contact with each other.

2. Description of the Prior Art Aluminum and many of its alloys have poor sliding or frictional behavior against themselves and other metals. This may be attributed to the fact that aluminum has a high surface energy and strong alloyingtendencies which allow it to bond readily with other metals. Moreover, since it is soft and ductile and its crystal contains a large number of slip systems, large contact areas can be produced, thus increasing the tendency to weld and to surface flow. Although aluminum surfaces often are covered with an oxide coating, and oxide coatings are known to be a significant factor in preventing surface damage by friction or sliding, the oxide film of aluminum is hard and brittle and, being on a soft substrate, is easily fractured. As soon as the adherent protective oxide film is broken, cold welding and sintering of the exposed sliding metal can occur. Even under lubricating conditions, sliding, contacting metallic surfaces are characterized by frequent metal-to-metal contact across the lubricant film. Aluminum and its alloys are particularly susceptible to galling or surface damage, usually with metal transfer, under such circumstances Because of its poor frictional behaviour, aluminum has not been used extensively in machines and loadbearing systems where one or more aluminum parts are in sliding contact with other parts, even under conditions of boundary lubrication. Such use of aluminum would be desirable because of its light weight and relatively low cost. In many applications where aluminum is used, protective coatings or liners are employed, the coating or liner beinga metal not subject to the aforesaid defects. For example, in a rotary pump of the sliding vane or 2-or 3 lobe type, a liner or coating is used inside the shell to prevent galling of the aluminum, rapid wear of aluminum whichdestroys effective sealing contacts, and binding of the rotating parts by metal transfer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a mechanical system having opposing contacting surfaces, one of which is aluminum, and means for frictionally moving the surfaces. Another object is to provide such a system wherein a fluid film is present between the sur faces. Still another object is to provide'such a system wherein the movement of the surfaces can be carried out under boundary lubricating conditions. A further object is to provide an aluminum based mechanical system having opposing surfaces capable of frictional movement, which system does not require a liner or coating on the aluminum based surface. In summary, these and other objects are fulfilled by means of an improvement in a system capable of mechanical operation and comprising a first part presenting an aluminum surface, a second part presenting a second surface designed to be in repeating sliding contactwith the aluminum surface, and means to induce and maintain the aluminum surface and the second surface in sliding relation to each other during the operation of the system, the improvement consisting of providing a second surface which is a metallic surface consisting of an alloy containing at least atom percent of at least two heavy metal transition elements, the ratio of the atomic radii of the largest to the smallest of the heavy metal transition elements being in the range IDS-1.68. and consisting of lO-lOO volume percent of a hard phase and 0-90 volume percent of a matrix phase which is softer than the hard phase, said hard phase containing a major fraction of Laves phase in such amount as to provide at least 10 volume percent thereof in the alloy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 depicts a test apparatus such as that employed in the examples to evaluate alloys. As a test apparatus it represents an embodiment of the mechanical system of this invention when it comprises a first part presenting an aluminum surface, a second part presenting a surface of alloy as defined herein, which surface is capable of being maintained in sliding contact with the aluminum surface of the first part, and means for inducing and maintaining the two surfaces in sliding contact with each other. FIG. 2 depicts a crosssectional view through the rotor axis of a pump with a rotatable sliding vane assembly embodying peripheral sliding contact between sliding vanes and the pump shell. FIG. 3 depicts a cross-sectional view through the rotor axes of a pump with a two-lobe cooperating contrarotating assembly embodying sliding contact between the lobes and the pump shell. FIG. 4 depicts a cross-sectional view through the rotor axes of a pump with a three-lobe cooperating contrarotating assembly embodying sliding contact between the lobes and the pump shell. FIG. 5 depicts a sectional view along a common axis of a cylinder and an enclosed piston embodying a sliding contact between them. FIG. 6 depicts a sectional view along a common axis of a cylinder and an enclosed piston ring embodying a sliding contact between them.

' DETAILED DESCRIPTION OF THE INVENTION It has been found that when a surface of an aluminum based metal is in sliding contact with a surface comprisingan alloy as defined herein, the aluminum based metal suffers little wear and surface damage. In many cases, the coefficient of friction of the aluminum based metal is surprisingly low, often as low as conventional bearing metals, against such alloys. This invention is applicable to a wide variety of mechanical systems characterized by two or more parts in repeating sliding contact with each other during system operation, especially when boundary lubrication conditions exist at the contact. Boundary lubrication can exist when sliding speeds are so low and contact pressures so high that the existence of load-supporting hydrodynamic wedges of lubricant are physically impossible. Sliding contact can after, as the other surface. Either part can be movable or fixed in place provided that at least one in each couple is movable, that is, able to move in sliding contact with the other. Maintenance of movement between the surfaces can be by a variety of means. Included are such means that can provide timed intermittent sliding contact between surfaces of two moving cooperating parts, that can provide oscillatory or reciprocatory sliding contact between two parts, only one of which may be moving, and that can provide sliding contact between one surface in a repeated circular sliding motion along the other surface.

In accordance with this invention, the alloy based surface in the mechanical system can be provided in any known, convenient suitable manner. For example, it can be the surface of a part which is made entirely from the alloy. It can be a separate preformed alloy layer mechanically attached to an underlying surface or bonded thereto according to known techniques. It can be obtained'by thermal diffusion of the alloy onto the base part by known techniques, for example, as disclosed in U.S. Pat. No. 3,331,700. Other known processes for obtaining the alloy based surface include weld overlaying, plasma arc spraying, powder metallurgy and casting. Surfaces of Laves phase-containing alloys should be sufficiently deep to allow for the wear acceptable to the mechanical system in which it is used. As a coating, this thickness usually is 0.001-0.40 inch, according to the size of the mechanical system in use, preferably, 0.0020.03 inch. Overlays anchored by welding or mechanical attachment usually are at least 0.125 inch.

It is essential that the alloy composition of the surface which is in sliding contact with aluminum based metal comprise a hard phase containing a major amount of a Laves phase as disclosed above. In most alloys comprising a hard phase and a soft phase the hard phase is substantially all Laves phase. In some alloys the hard phase contains a major fraction, that is, greater than 50 volume percent, of Laves phase and a minor fraction, that is, less than 50 volume percent, of another hard phase which accompanies the Laves phase, often surrounding it. For example, in certain alloys consisting essentially of Co, Mo, Si and Cr, especially when the Cr content is at least 12 weight percent, the Lavesphase is surrounded by another hard phase. The surround is present as a minor fraction, usually less than 25 volume percent, of the hard phase. A Laves phase contains one or more metallographic constituents that have the C (hexagonal), C (cubic) or C (hexagonal) crystal structure as described in International Tables for X-Ray Crystallography, Symmetry Groups N. F. M. 3

Henry and K. Lonsdale, International Union of Crystallography, Kynoch Press, Birmingham, England (1952). Prototypes of the Laves phase crystal structures are, respectively, MgZn MgCu; and MgNi Such phase structures are unique crystal structures that permit the most complete occupation of space by assemblages of two sizes of spheres. Fundamentally, the Laves phase can be represented by the formula AB the large atoms A occupying certain sets of crystallographic sites and the small atoms B occupying other sites, in which the ratio of atomic radii AB is in the range 1.05-1.68. Laves phases occur as intermediate phases in numerous alloy systems. Laves phases generally have a homogeneity range, that is, they can have any of a range of elemental compositions while maintaining their characteristic crystal structure. The atom ratio B:A can form slightly less to slightly more than .2, possibly the result of some vacant sites in the crystal structure. Also, more than one kind of atom can occupy the large atom sites, the small atom sites, or both. Such Laves phases can be represented stoichiometrically by the formula (A C,)(B ,,D,,) 2 where C represents the atoms of one or more kinds that substitute for the large atoms, D represents the atoms of one or more kinds that substitute for the small atoms, of the binary Laves formula A8 and x and y have values in the range 0-1.

An alloy, as the term is used herein, is a substance having metallic properties and containing in its clemental composition two or more chemical elements of which at least two are metals; other elements can be present. A heavy metal transition element is a metal selected from the group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Mn, Re, Cr, Mo, W, U, V, Nb, Ta, Ti, Zr, I-If, Th, Sc, Y, La, Zr and Ce.

Numerous binary and higher Laves phases which are suitable for purposes of the invention and containing at least two heavy transition metals are disclosed in the prior art. For example, binary and ternary Laves phases are shown in Alloy Chemistry of Transition Elements, M. V. Nevitt, pages 101-178, especially Tables XIII and XIV, appearing in Electronic Structure and Alloy Chemistry of the Transition Elements, P. A. Beck, lnterscience Wiley, New York, N.Y., 1963. Typical alloys consisting largely or entirely of ternary and higher Laves phase are disclosed in Table I.

Generally, in the hard phase-containing alloys useful in this invention the transition metal elements are selected from the group consisting of V, l-lf, W, Ta, Nb, Mo, Ni. Co, Fe, Mn, Cr, Zr and Ti. Preferably, the hard phase-containing alloy consists essentially of a substantial amount of at least one metal A, a substantial amount of at least one metal B and Si, metal A being selected from Mo and W and metal B being selected from Fe, Cr, Co and Ni, the sum of the amounts of metals A and B being at least 60 atom percent of the alloy, the amount of Si and the relative amounts of metals A and B being such as to ensure that 10-100 volume per- I cent of the alloy is hard phase, the hard phase being distributed in a relatively soft matrix of the remaining 0-90 volume percent of the alloy. More preferably, 20-85 volume percent of the hard phase (containing at least volume percent, and preferably, substantially all, Laves phase) is distributed in 15-80 volume percent of matrix phase. The matrix can be formed of the same alloy system as the hard phase; it can be a single metal, a solid solution, one or more intermetallic compounds other than Laves phase or a mixture of solid solution and said intermetallic compounds. It must be softer than the hard phase and, generally, should have no more than about 50 percent of the Knoop hardness of the hard phase. Preferred metal matrix phases exhibit a Knoop hardness of 350--750.

Cobalt based alloys useful herein and having the requisite amount of hard (including Laves) phase include those disclosed in U.S. Pat. Nos. 3,180,012 and 3,410,732. Alloys containing silicon and at least two heavy transition elements selected from the group consisting of Mo, Co, W, Ni and Cr include those disclosed in U.S. Pat. No. 3,361,560.

Other hard, substantially 100 percent Laves phasecontaining alloys useful herein include those disclosed in Tables 11 and 111 (the latter preferred) wherein the elements are expressed in weight percent and the hard phases are expressed in volume percent.

vrsiis tenTperaturdof at least 250C. and a room temperature modulus of at least 300,000 p.s.i., for example, phenol-formaldehyde resins, aromatic polyimides, aromatic polyamides, aromatic polyketones, aromatic polythiazoles and polybenzotriazoles. Binders can comprise up to 90 percentof the bindel alloy mixture.

TABLE 11 ance to 100 percent): alloy 1000 (greater than 99.6% 0 A1); 2024 (4.5% Cu, 1.5% Mg, 0.6% Mn); 2218 (4% CO Ni M0 Si Fe Mn Other Hard Phase 2 g); 4032 (125% 1% g (19% Cu, 0.9% Ni); 5154 (3.5% Mg, 0.25% Cr); 6061 (1% gg 3g 18 Ge ;3 Mg, 0.6% Si, 0.25% Cu, 0.25% Cr); A13 12% st 10 -36 18 v36 60 A132 (12% Si, 2.5% Ni, 1.2% Mg, 0.8% Cu); and 40E 45 58 Z; 25 (5.5% Zn, 0.6% Mg, 0.5% Cr, 0.2% Ti). Preferred al- 38 O 52 Ta 35 loys include 1000, 2024, 2218 and 40E as well as 5456 60 10 30 Ti 25 (5% Mg, 0.7% Mn, 0.15% Cu, 0.15% Cr); 142 (4% Cu, 3; 35331 33 2% Ni, 1.5% Mg); and 195 (4.5%Cu). A116 2024 is espec1ally preferred TABLE 111 Knoop Hardness Co Ni Mo W Si Cr C Hard Phase l-lard Phase Matrix 59.7 27.9 4.0 7.9 0.5 60 1481 569 57.6 27.8 2.0 12.0 (1) 40 920 450' 62.0 28.0 2.0 8.0 (2) 40 1481 735 70 28 2 1039 3) 65 10 50 1039 (3) 65 29 6- 50 1039 (3) 65 33 2 50 1039 (3) 60 30 10 58 1220 (3) 60 34, 6 65 4 950 3 60 33 2 50 1039 3) 55 35 10 65 1231 (3) 55 39 6 78 1200 3) 55 41 4 85 954 3) 55 43 2 75 900 (3) 50 48 2 76 l 1443 3 55 35 10 65 824 316 53 35 3 9 55 1170 370 51 9 40 45 15 35 44 6 75 58 35. 7 go (l) 0.6 Mn instead of carbon (2) 0.01 B and 0.2 Zr instead of carbon 3) Less than that of the Hard phasmgenerally. 350750 The alloy based surface can be 100 percent of the de- Anodized aluminum is also operable in this invention fined alloy or a mixture of the alloy and a binder which binds the alloy in place without destroying its Laves phase. Binders should be inert to, that is, nonreactive with, and softer than the'Laves phase of the alloys they q iron alloys. Resins include phenolic resins and essentially linear resins having a second ordertransition temperature (as determined by plots of flexural modulus as the aluminum based surface. The depth of the anodized layer is easily determined by test and typically is in the range2,000 microinches; generally, it is in the range 3001,200 microinches.

The mechanical systems of this invention containing two opposing surfaces can be used in many instances in the absence of a lubricating agent; in other words, they are self-lubricating. Examples of such an application include an air control valve which must have no contact of air with lubricant and a Corliss or slide valve for steam engine operation.

The mechanical-systems of this invention also are operable in the presence of non-lubricating fluids, such as elongated contact across the direction of slide, the

contact separating two bodies of fluid. Sucha contact exists between a cylinder and an enclosed piston or piston ring designed toslide on a common axis. It can also be found in rotary pumpsof the vaned, 2-lobe and 3- lobe types between the interiors of the curved shells and the sealing wipers on the rotating parts. Such pumps include rotatable sliding vane assemblies, 2-lobe contrarotating assemblies and 3-lobe contrarotating assemblies. The sliding couples obtainable by this invention can be used in airor liquid-driven rotary devices for converting fluid energy to mechanical power. The present invention provides an alternative to the use of slide surfaces in such mechanical systems which heretofore comprised non-galling materials or shells of aluminum protected by liners of non-galling materials. Sliding couples obtainable by means of this invention retain their ability to maintain the separation of fluid bodies without galling or rapid wearing of the aluminum. The present invention makes possible the simplification of pump designs, expansion of choice in the selection of useful materials, especially lighter materials, and reduced construction costs.

DETAILED DESCRIPTION OF THE DRAWINGS In the test apparatus represented by FIG. 1 holder 1 is anchored to a fixed reference (not shown) and holds test plate 2 level and in place by means not shown. Holder 1 contains electrical cartridge heaters,-below test plate 2, which maintain elevated plate temperatures where desired. Holder 1 has containing capacity, above test plate 2, in which lubricating or other liquids can be maintained during tests. Pin 3 is circular bar stock of the material used in sliding test against the sur face of plate 2 while the pin end surface is horizontal. Pin 3 is held vertically positioned by clamp 4 and clamp tightening means (not shown). Clamp 4 is integral with one end of reciprocating bar 5. Bar 5 has yoke 6 at its other end and is guided in horizontal linear motion by bushings 7 and 8, both anchored to said fixed reference. Yoke 6 is linked to oscillating means of controlled frequency and stroke. Load bearer 9 is level on top 'of clamp. 4, is positioned perpendicular to the movement direction of bar 5 and has the axis of its pivot hole 10 normal to the plane of plate 2. It is long enough that it swings less than 10 degrees over the oscillating range of bar 5 and its fit at the top of clamp 4 corresponds to a single plane. Weights (not shown) are loaded on top of load bearer 9, centered by the pin 3 axis to the extent needed to produce the desired pressure on the bottom end of pin 3. The manner of using this apparatus is described in the examples.

FIG. 2 depicts a pump with a line contact across the directionof sliding between the pump shell and the sur- 16 in communicating relation with inlet 17 and outlet 18. Cylindrical rotor 19, having vane slots 20, 21, 22 and 23, is provided with radial vanes 24, 25, 26 and 27 biased radially outward (by means not shown) against the periphery of chamber 16. The center of rotor 19 is displaced so that space between it and chamber 16 is carrier space for fluid entering inlet 17 to be carried by adjacent vanes to outlet 18. Shell 15 and rotor 19 are of an aluminum based metal. Vanes 24, 25, 26 and 27 are of a Laves phase-containing alloy as described herein and they freely slide radially toward and away from the rotor during its rotation to keep them in continuous sliding contact with the periphery of chamber 16 during pump operation.

FIG. 3 depicts a pump with a line contact across the direction of sliding contact between the pump shell and the lobes of a two-lobe cooperating contrarotating assembly. Rotors 31 and 32 are viewed through their parallel axes. They rotate in opposite directions in cooperation with gears (not shown), one on each rotor shaft, intermeshed with each other. The rotors rotate in overlapping cylindrical chambers which communicate with inlet 33 and outlet 34 inside shell 35 which is of an aluminum based metal. Rotors 31 and 32 are coated on their exterior surfaces 36 and 37 with a Laves phasecontaining alloy as described herein and they are in sliding contact with each other and with shell 35 at its internal periphery and at its cylindrical ends.

FIG. 4 depicts a pump with a line contact across the direction of sliding contact between the pump shell and the lobes of a three-lobe cooperating contrarotating assembly. Rotors 41 and 42 are viewed through their parallel axes. They rotate in opposite directions in cooperation with gears (not shown), one on each rotor shaft, intermeshed with each other, inside aluminum based metal shell 43. Shell 43 is internally shaped to provide overlapping cylindrical chambers 44 and 45 communicating with inlet 46 and outlet 47. Rotors 41 and 42 are in close sliding contact with each other and with the internal surface of shell 43. They are coated on their exterior surfaces 48 and 49 with a Laves phase-containing alloy as described herein.

FIG. 5 depicts a sectional view along the axis of a cylinder and an enclosed piston designed to slide on a common axis. Piston 51 fits sealably inside cylinder 52 and is axially movable therein. Piston 51 has coating 53 of a Laves phase-containing alloy as described herein around its periphery. Coating 53 provides an elongated contact across the direction of piston slide which separates fluid body 54 from fluid body 55.

FIG. 6 depicts a sectional view along the axis of a cylinder and an enclosed piston ring. Piston 63 fits inside cylinder 56 in a loosely scalable fit and is axially movable therein. Piston 63 has annular grooves which support piston rings 57, 58 and 59 sealably inside cylinder 56. The peripheries of rings 57, 58 and 59 have coatings 6t), 61 and 62 of a Laves phase-containing alloy as described herein. These coatings provide an elongated contact across the direction of slide'which separates fluid body 64 from fluid body 65.

In the following examples percentages are by weight,

unless otherwise noted.

Example 1 P Performance With Lubricating Oil This example tests sliding contact under boundary lubrication conditions between the contacting surfaces. 0.375 lnch diameter pins having polished flat ends were files of the coupons were measured using a profilometer. Each pin was mounted'in an oscillatory mechanism so that it could be drawn back and forth at sinusoidally variable speed in 0.5 inch strokes while its flat end was in constant and complete contact with a flat sintered coating of a coupon. The contact area was submerged in a TOW-40 base hydrocarbon oil. Each pin was loaded to 1000 p.s.i. pressure against the plate and oscillated at feet per minute average velocity. Friction was measured during the oscillation. The system was operated at room temperature until the friction was constant, about 15 minutes. Thereafter, the system was heated to 38C., run for 5 minutes at that temperature,- and its friction was again measured. At 28C. intervals, this procedure was repeated until 204C. was reached. At 204C. the test was continued for 30 minutes. The system was then cooled and the coated coupon and pin specimens were removed and heated to 232C. for 24 hours to'drive off oil. Each pin was weighed to determine its weight change and the surface profile along the friction path of each corresponding coated coupon was I again measured with a profilometer to determine the amount of surface damage produced.

The pins also were tested against the surfaces of flat 0.25 inch by l X 2 inch blocks of metals having the fol- 5 lowing compositions: machined from solid rodof the following materials:

- G. M2Tool Steel, havin the corn osition 0.85 er- A. Alloy 2024-T4 (Alloy 2024 solution heattreated Cent carbon 4 percentgchmmiurg, 2 percent g accorimg to test prqcedure of Metals Hand dium, 6.25 percent tungsten, 5 percent molybdebook prqpemes Selecuon of Metals num and the balance iron. This is a commonly used ggLggnan, American Society For Metals, page 10 wear resistant pump Shaft materiaL H. 416 Stainless Steel, a martensitic free machining 3 2 g g f fi g on Its steel often used for machine parts and pump shafts; at en a ept O 0 mlcromc having the composition 12-14 percent chromium, e Bronze SAE 59 a common bearmg 1 0.15 percent maximum carbon, 0.06 percent maxiterial hav ng the composition 83 percent copper, 7 mum phosphorus! 1 percent maximum sulfur percent tin, 7 percent lead and 3 percent zinc. the balance to 100 percent iron Bronze SAE a Common bearmg matenal Table IV shows the test data obtained. In the table havmg the eempostlon 3 Percent Copper 10 the coefficient of friction is the ratio of the applied drag Cent tm 0 2 P (or force tangent to the load) to the pin load (or force 1 Inch by 2 h couponsef 410 stemless Steel were normal to the load). The CLA value is the center line Plasma lf 0015 meh eeatmgs P one of h average of variations in surface height along a line of metals desenbed below- The spfayed coatings were measurement across the direction of sliding contact on Pered and ground to a thickness of the coupon or block as measured by the profilometer. The metals were: It is expressed as the arithmetic average. in micro- An ll y of Fobalt, 35% molybdenum and 25 inches, of deviations from a plane. Visual ratings were 10% l of whleh by Volume was Laves based on observations of 6.6X photographs of tracks Phase and 35% by Volume was mam) Phase rubbed by the pins and of direct 10X viewing of the F. A mixture of percent of the alloy of E and 20 tracks using the l percent nickel. The nickel acted as a binder for the 1 N0 i ibl Score marks alloy after sin ering- 3O 2 A few visible score marks Tpe..l1l .l$ were welghed and the coated Surface P 3 Signs of seizure or transverse microcracks. M

TABLE IV Coefficient of Friction Pin Wt. CLA Flat After Change Before After Pin Face Highest Lowest Test (Gram) Test Test Visual Rating A E 0.25 0.19 0.23 -.0037 7.0 80.0 2 13 E 0.15 0.11 0.11 +.0036 9.5 10.0 1 C E 0.28 0.18 0.22 -.0011 10.0 9.5 1 D E 0.21 0.13 0.18 .0009 10.0 14.5 2 A F 0.27 0.14 0.18 .0034 8.0 14 2 B F 0.21 0.13 0.18 +0031 11.0 21.0 1 C F 0.29 0.23 0.23 .0067 9.0 14.5 1 D F 0.28 0.19 0.19 -.00O6 9.0 9 2 A 6 0.37 0.28 0.29 2.5 7.0 3 A H 0.25 0.21 0.21 .0014 11.5 40.0 3

It can be seen that under boundary lubrication conditions, an aluminum surface rubbing against a Laves phase-containing alloy surface is comparable to and parable to that of generally used bronze bearing materials and less than that of a frequently used steel.

Example 2 Performance with Water and Wet Steam This example tests sliding contact with a nonlubricating fluid between the contacting surfaces. Pins were prepared as in Example 1 from materials A-D. As in Example 1, coupons were prepared and coated with metal F. The pins also were tested against the surfaces the test data obtained.

of flat 0.25 inch by l by 2 inch blocks of metal cast from 1. An alloy of 62 percent cobalt, 28 percent molybdenum, 8 percent chromium and 2 percent silicon, of which 50 percent by volume is Laves phase and 50 percent by volume is matrix phase. Each pin was mounted in the mechanism of Example 1 with its flat end in constant and complete contact with the sintered coating of a coupon or the flat face of a block. The contact area was submerged in water. At 10 1000 p.s.i. pin end loading and at S'feet per minute average velocity, the system was operated at room temperature until constant friction was achieved, about minutes. Thereafter, the system was heated to 38C., I run for 5 minutes at that temperature and its friction 15 was measured. At 14C. intervals, this procedure was repeated until 93C. was reached. At 100C. the test was continued 30 minutes, with friction measurement at 5 minute intervals as the water boiled. The system was then cooled and the block and pin specimens were removed and heated to 149C. to drive off water. The pin and block or coated coupon of each combination were weighed to determine their weight changes. The flat face profiles of the blocks and coated coupons were measured across the rubbing paths of the pins to determine changes in those surfaces. The visual ratings of the rubbed parts of the flat faces were also determined employing the scale used in Example 1. Table V shows the two surfaces in sliding contact with each other, the improvement consisting of employing as the first surface an aluminum based surface and as the second surface a metallic surface comprising an alloy containing at least 60 atom percent of at least two heavy metal transition elements, the ratio of the atomic radii of the largest to the smallest transition elements being 1.05 l.68, and consisting of 10-100 volume percent of a hard phase and 0-90 volume percent of a matrix phase which is softer than the hard phase, said hard phase containing a major fraction of Laves phase in such amount as to provide at least 10 volume percent thereof in tlre a lloy I W V H M 2. The system of claim 1 wherein the aluminum suri EEPQQ ZEQ.-... a 3. The system of claim 1 wherein the second surface is a mixture of alloy and a binder which is inert to and 2521!... 2 52111 9 ave P 1 9f tha y- 4. The system of claim 1 wherein the alloy based surface a thickness of 0.001:0.40 inch. p 5. The system of claim 1 wherein the two surfaces are in operational sliding contactwith each other.

6. The system of claim 5 wherein the sliding contact is an elongated contact across the direction of the slide andt he sliding contact separates two bodies of fluid.

7. The system of claim 1 wherein the transition elements are selected from the group consisting of V, Hf, W, E Qb, Mo, Ni, Co, Fe, Mn, Cr, Zr and Ti.

TABLE V CLA Flat Coefficient of Friction Wt. Change (Gram) Before After Pin Face Highest Lowest After Test Pin Block Test Test Visual Rating A F 0.44 0.21 0.38 .00l7 -.0020 9.2 7.5 B F 0.52 0.18 0.44 +.0002 +0080 8.0 6.0 l C F 0.18 0.11 0.18 -.00l4 +.00l2 10.0 8.0 1 D F 0.23 0.11 0.23 -.0O16 0010 10.0 11.0 1 A H 0.62 0.43 0.59 .O030 10.0 20.0 3 A l 0.64 0.50 0.50 .0033 .0010 4.0 2.5 1. B l 0.85 0.49 0.81 +.0015 +.0003 7.5 3.5 2 C l 0.37 0.15 0.36 .0004 +0003 7.0 4.5 l D l 0.32 0.16 0.32 -.0006 +0003 70 9.0 3

The results show that under the poor lubricating conditions provided by water the surface damage toLaves 1. An improved mechanical system comprising a first part presenting an aluminum surface, a second part presenting a second surface in contact with the alumiv num surface, and means for inducing and maintaining 8. The system of claim 7 wherein the hard phasecontaining alloy consists essentially of a substantial amount of at least one metal A, a substantial amount of at least one metal B, and Si, metal A being selected from Mo and W, metal B being selected from Fe, Cr, Co and Ni, the sum of the amounts of A and B being at least 60 atom percent of the alloy.

9. The system of claim 8 wherein the amount of Si and the relative amounts of A and B are such'that 20-85 volume percent of hard phase is distributed in l5-80 volume percent of matrix phase.

110. The system of claim 9 wherein the hard phase is 

1. An improved mechanical system comprising a first part presenting an aluminum surface, a second part presenting a second surface in contact with the aluminum surface, and means for inducing and maintaining the two surfaces in sliding contact with each other, the improvement consisting of employing as the first surface an aluminum based surface and as the second surface a metallic surface comprising an alloy containing at least 60 atom percent of at least two heavy metal transition elements, the ratio of the atomic radii of the largest to the smallest transition elements being 1.05 -1.68, and consisting of 10-100 volume percent of a hard phase and 0-90 volume percent of a matrix phase which is softer than the hard phase, said hard phase containing a major fraction of Laves phase in such amount as to provide at least 10 volume percent thereof in the alloy.
 2. The system of claim 1 wherein the aluminum surface is anodized.
 3. The system of claim 1 wherein the second surface is a mixture of alloy and a binder which is inert to and softer than the Laves phase of the alloy.
 4. The system of claim 1 wherein the alloy based surface has a thickness of 0.001-0.40 inch.
 5. The system of claim 1 wherein the two surfaces are in operational sliding contact with each other.
 6. The system of claim 5 wherein the sliding contact is an elongated contact across the direction of the slide and the sliding contact separates two bodies of fluid.
 7. The system of claim 1 wherein the transition elements are selected from the group consisting of V, Hf, W, Ta, Nb, Mo, Ni, Co, Fe, Mn, Cr, Zr and Ti.
 8. The system of claim 7 wherein the hard phase-containing alloy consists essentially of a substantial amount of at least one metal A, a substantial amount of at least one metal B, and Si, metal A being sElected from Mo and W, metal B being selected from Fe, Cr, Co and Ni, the sum of the amounts of A and B being at least 60 atom percent of the alloy.
 9. The system of claim 8 wherein the amount of Si and the relative amounts of A and B are such that 20-85 volume percent of hard phase is distributed in 15-80 volume percent of matrix phase.
 10. The system of claim 9 wherein the hard phase is substantially all Laves phase. 